1. Field of the Invention
The invention relates to a process for preparing organofunctionalized solids, particularly organofunctionalized metal oxides, and to solids and metal oxides prepared by the process.
2. Background Art
Surface modification of solids, whether they be pulverulent or mass (bulk) solids, is frequently confronted by the problem that the surface modification is not permanent, i.e., the surface modification agent is not sufficiently anchored to the surface and, therefore, can become detached and washed away by solvent, the surrounding medium, or the surrounding matrix. This problem can be overcome by obtaining a firm chemical attachment involving the formation of chemical bonds, as has been disclosed in EP 896029 B1, for example. But the latter approach then has the disadvantage that the known processes necessitate high temperatures and long reaction times, which in the case in particular of modifying agents that carry reactive organic groups such as methacrylate, epoxy or isocyanate groups can lead to decomposition reactions, and thus an unwanted reduction in the amount of functional groups and to the formation of reaction byproducts which impair the quality of the modified metal oxides, particularly those used as filler.
Reaction byproducts and a loss of functional groups are especially disadvantageous when the solid is surface-treated with the aim of improving its adhesion or crosslinking with the surrounding medium, since such byproducts can alter the adhesion or crosslinking uncontrollably and since crosslinking reactions are sensitively dependent on precise compliance with the stoichiometry of the reactive groups. Reaction byproducts are also particularly disadvantageous when the pulverulent solid is used as a rheological additive in liquid media such as polymers, resins, or resin solutions, since such reaction byproducts can alter the rheology uncontrollably. Reaction byproducts are further particularly disadvantageous when the pulverulent solid is used as a free-flow aid and triboelectric charge control agent in pulverulent systems such as toners, developers, powder coating materials or coating systems, since such reaction byproducts may alter the free flow and triboelectric effects unpredictably.
The addition of Lewis acid or Lewis base catalysts to accelerate the reaction of silica with alkoxysilanes and to improve the reaction yield of silica with alkoxysilanes is known. It has the disadvantage, however, that the catalysts, although they accelerate the binding reaction of the modifying reagents, also frequently catalyze the decomposition reactions of the functional groups.